Conventional internal combustion engines are configured with spark plugs which contain two electrodes. A powered electrode is mounted within an insulator sleeve to have one end located within the cylinder. A ground electrode is configured to be opposed across an air gap with respect to the powered electrode. Such spark plugs are unitary in nature, since they contain both electrodes in a single unit.
In some cases, spark plugs have been combined with fuel injectors to inject fuel through a nozzle into air gap portion of the spark plug. Such combinations also are unitary in nature since they contain the spark plug elements and fuel injector elements in a single unit.
In each case, the location within the combustion chamber of the spark generated across the arc gap is limited by the relatively short length of the spark plug body extending into the combustion camber. In addition, because of the split nature of how a conventional ignition coil is used, the ignition voltage and current capacity dictates that the arc gap be relatively small. This, in turn, allows for a correspondingly small spark.
In some two-cycle engines, such as the Internal Combustion Engine With A Single Crankshaft And Having Opposing Cylinders And Opposing Pistons in each cylinder (“OPOC engine”) described in U.S. Pat. No. 6,170,443 and incorporated herein by reference, the combustion chamber is formed by opposing pistons which converge towards each other during the compression stroke. In such an engine that has no cylinder head, the mounting of a conventional spark plug is limited to the side of a cylinder. Depending on the diameter of the cylinder, the spark gap is usually located to one side and therefore off-center to the formed combustion chamber. When an off-center spark location is used, accommodations have to be made to the engine. For instance, special piston face configurations are required in order to approach an even distribution of combustion forces across each piston face.